Valve structure of shock absorber

ABSTRACT

A valve structure includes a piston valve assembly, and a frequency unit including a hollow housing, a free piston and an auxiliary valve assembly. The piston valve assembly, installed at one end of a piston rod, operates with the inside of a cylinder being divided into upper and lower chambers, and generates a damping force varying according to a moving speed. The frequency unit moves together with the piston valve assembly and generates a damping force varying according to a frequency. The housing is mounted at a lower end of the piston rod such that the housing is disposed under the piston valve assembly. An inner space of the housing is partitioned into upper and lower spaces by the free piston. The free piston is disposed to be vertically movable within the housing. The auxiliary valve assembly is mounted at a lower end of the housing.

CROSS-REFERENCE(S) TO RELATED APPLICATION

This application claims priority of Korean Patent Application No.10-2011-0072634, filed on Jul. 21, 2011, in the Korean IntellectualProperty Office, which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve structure of a shock absorber,and more particularly, to a valve structure of a shock absorber which iscapable of controlling respective damping forces at a small amplitudeand a large amplitude in compression and rebound motions of a pistonvalve, thereby satisfying both the ride comfort and the controlstability.

2. Description of the Related Art

In general, a suspension is installed in a vehicle to dampen a shock orvibration transferred from a road surface to an axle during driving. Asone example of such a suspension, a shock absorber has been used.

A shock absorber operates according to a vibration of a vehicle causedby a state of a road surface. In this case, a damping force generated inthe shock absorber varies according to an operating speed of the shockabsorber, that is, a fast or slow operating speed thereof.

A vehicle ride comfort and a steering stability may be controlledaccording to how to adjust a characteristic of a damping force generatedin a shock absorber. Therefore, in designing a vehicle, it is veryimportant to adjust a characteristic of a damping force of a shockabsorber.

A conventional piston valve is designed to have a constant dampingcharacteristic at a high speed, a middle speed, and a low speed due tothe use of a single flow passage. Therefore, when intending to improve aride comfort by reducing a low-speed damping force, middle-speed andhigh-speed damping forces may also be affected. In addition, aconventional shock absorber has a configuration in which a damping forcevaries according to a change in a speed of a piston, regardless of afrequency or a stroke. In the case of the damping force varyingaccording to only the change in the speed of the piston, the samedamping force is generated even in various states of the road surface.Therefore, it is difficult to satisfy both the ride comfort and thesteering stability.

Accordingly, there is a need for continuously conducting research anddevelopment on a valve structure of a shock absorber which can vary adamping force according to various road conditions, such as a frequencyand a stroke, thereby satisfying both the vehicle ride comfort and thesteering stability.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to provide a valvestructure of a shock absorber, which includes a main piston valveconfigured to generate a damping force varying according to a movingspeed of a piston, and a frequency unit configured to generate a dampingforce varying according to a frequency, thereby satisfying both thevehicle ride comfort and the control stability.

According to another embodiment of the present invention, a valvestructure of a shock absorber, which has a cylinder filled with aworking fluid and a piston rod having one end located inside thecylinder and the other end extending outward from the cylinder,includes: a main piston valve assembly installed at one end of thepiston rod and configured to operate in a state that the inside of thecylinder is divided into an upper chamber and a lower chamber, andgenerate a damping force varying according to a moving speed; and afrequency unit configured to move together with the main piston valveassembly and generate a damping force varying according to a frequency,wherein the frequency unit includes: a hollow housing mounted at a lowerend of the piston rod such that the housing is disposed under the mainpiston valve assembly; and a free piston disposed to be verticallymovable within the housing.

The frequency unit may include an auxiliary valve assembly mounted at alower end of the housing.

A flow of a working fluid pressurizing the free piston and a flow of aworking fluid passing through the free piston and flowing to an oppositeside of the free piston may be formed as a single flow.

An inner space of the housing may be partitioned into an upper space anda lower space by the free piston.

The upper space may communicate with the upper chamber through aconnection passage formed inside the piston rod, and the lower space maycommunicate with the lower chamber through the auxiliary valve assemblyamounted at the lower end of the housing.

The free piston may have a through-hole that is opened during alow-frequency compression to allow the working fluid to flow from thelower space to the upper space, and when no external force is applied,the through-hole may maintain a state closed by a valve body.

A lip portion made of a rubber may be integrally formed on an outercircumferential surface of the free piston, and the lip portion mayclosely contact an inner surface of the housing.

A stepped portion limiting the movement of the free piston may be formedon an inner surface of the upper space of the housing. A plurality ofgroove portions may be formed on an inner surface of the lower space ofthe housing. An intermediate portion having an internal diametersubstantially equal to an external diameter of the free piston may beformed between the stepped portion and the groove portion.

The frequency unit may include an inner tube installed inside thehousing to open or close a flow passage in cooperation with the freepiston.

The inner tube may include at least one of a convex portion, a concaveportion, a hole, or a cut-out portion, such that a passage communicatingthe upper chamber with the lower chamber within the cylinder is openedor closed according to a vertical movement of the free piston within thehousing.

The inner tube may include at least one upper concave portion, which isconcavely formed on an inner surface of the inner tube, and at least onelower concave portion, which is not connected to the upper concaveportion and is formed in a straight line with the upper concave portion,and when no external force is applied, the free piston may be locatedbetween the upper concave portion and the lower concave portion.

The inner tube may include a ring-shaped concave portion that isconcavely formed on the inner surface in a ring shape, and when noexternal force is applied, the free piston may be located at a positionwhere the ring-shaped concave portion is formed.

The free piston may be supported by an upper elastic member and a lowerelastic member, such that the free piston moves vertically within theinner space of the housing according to a frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a valve structure of a shockabsorber according to the present invention.

FIG. 2 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber at a highfrequency according to a first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber at a lowfrequency according to a first embodiment of the present invention.

FIG. 4 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber at a lowfrequency according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber at a highfrequency according to a second embodiment of the present invention.

FIGS. 6A to 6D are perspective views of inner tubes having variousshapes according to the present invention.

FIG. 7 is a cross-sectional view showing a valve structure of a shockabsorber according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber in alow-frequency compression mode according to a third embodiment of thepresent invention.

FIG. 9 is a cross-sectional view showing main parts for describing afluid flow through a valve structure of a shock absorber in alow-frequency rebound mode according to a third embodiment of thepresent invention.

<Description of Reference Numerals> 10: cylinder 11: upper chamber 12:lower chamber 20: piston rod 21: connection passage 30: main pistonvalve assembly 31: main piston body 32: main compression passage 33:main rebound passage 35: main compression valve unit 37: main reboundvalve unit 39: band 100, 200, 300: frequency unit 110, 210, 310: housing120, 220, 320: free piston 130, 230, 330: inner tube 131: upper concaveportion 132: lower concave portion 140, 240, 340: auxiliary valveassembly 141, 241, 341: auxiliary valve body 142, 242, 342: auxiliarycompression passage 143, 243, 343: auxiliary rebound passage 145, 245,345: auxiliary compression valve unit 147, 247, 347: auxiliary reboundvalve unit 157, 257, 357: upper spring 158, 258, 358: lower spring 231:ring-shaped concave portion

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, valve structures of shock absorbers according to preferredembodiments of the present invention will be described in detail withreference to the accompanying drawings.

As shown in FIG. 1, a shock absorber having a valve structure accordingto the present invention includes an approximately cylindrical cylinder10 filled with a working fluid such as oil, and a piston rod 20 havingone end located inside the cylinder 10 and the other end extendingoutward from the cylinder 10.

The valve structure of the shock absorber according to the presentinvention includes a main piston valve assembly 30 and a frequency unit100. The main piston valve assembly 30 is installed in one end of thepiston rod 20. The main piston valve assembly 30 operates in a statethat the inside of the cylinder 10 is divided into an upper chamber 11and a lower chamber 12, and generates a damping force varying accordingto a moving speed. The frequency unit 100 moves together with the mainpiston valve assembly 30, and generates a damping force varyingaccording to a frequency.

The main piston valve assembly 30 and the frequency unit 100 aresuccessively installed at an end of the piston rod 20. The other end ofthe piston rod 20 is slidable along and liquid-tightly passes through arod guide and an oil seal, and extends outward from the cylinder 10.

The main piston valve assembly 30 may include a main piston body 31, amain compression valve unit 35, and a main rebound valve unit 37. Themain piston body 31 has at least one main compression passage 32,through which a working fluid passes during compression of the shockabsorber, and at least one main rebound passage 33, through which aworking fluid passes during rebound of the shock absorber. The maincompression valve unit 35 is disposed above the main piston body 31 togenerate a damping force against a pressure of the working fluid passingthrough the main compression passage 32. The main rebound valve unit 37is disposed under the main piston body 31 to generate a damping forceagainst a pressure of the working fluid passing through the main reboundpassage 33.

In addition, a Teflon band 39 may be installed on the outercircumferential surface of the main piston body 31 in order for closecontact with the inner circumferential surface of the cylinder 10 andprevention of friction.

The frequency unit 100 according to the first embodiment includes ahollow housing 110, a free piston 120, and an auxiliary valve assembly140. The inside of the housing 110 is empty, and the housing 110 ismounted at a lower end of the piston rod 20 such that it is disposedunder the main piston valve assembly 30. The free piston 120 opens orcloses a flow passage while moving within the housing 110. The auxiliaryvalve assembly 140 is mounted at a lower end of the housing 110.

The auxiliary valve assembly 140 includes an auxiliary valve body 141,an auxiliary compression valve unit 145, and an auxiliary rebound valveunit 147. The auxiliary valve body 141 has at least one auxiliarycompression passage 142, through which the working fluid passes duringcompression of the shock absorber, and at least one auxiliary reboundpassage 143, through which the working fluid passes during rebound ofthe shock absorber. The auxiliary compression valve unit 145 is disposedabove the auxiliary valve body 141 to generate a damping force against apressure of the working fluid passing through the auxiliary compressionpassage 142. The auxiliary rebound valve unit 147 is disposed under theauxiliary valve body 141 to generate a damping force against a pressureof the working fluid passing through the auxiliary rebound passage 143.A fixing member 144, including a rivet, a bolt, and a nut, is installedin the middle of the auxiliary valve body 141, such that the auxiliarycompression valve unit 145 and the auxiliary rebound valve unit 147 aredisposed above and under the auxiliary valve body 141.

The auxiliary valve body 141 of the auxiliary valve assembly 140 isfixed under the main piston valve assembly 30 by the housing 110. Theinner space of the housing 110, in particular, an upper space 111 abovethe free piston 120, may communicate with the upper chamber 11 through aconnection passage 21 formed inside the piston rod 20. The inner spaceof the housing 110 may be partitioned into the upper space 111 and thelower space 112 by the free piston 120.

The free piston 120 is installed to move vertically within the innerspace of the housing 110 according to a frequency (amplitude). The freepiston 120 is supported within the inner space of the housing 110 by anupper spring 157 as an upper elastic member and a lower spring 158 as alower elastic member. The upper elastic member and the lower elasticmember may be any one selected from a spring, a disk, and a clip. Theupper elastic member and the lower elastic member may be any member thatcan support the free piston 120 by elasticity. The upper spring 157 andthe lower spring 158 as the elastic members may be different in shape ormodulus of elasticity, and various modifications may be made in design.In the case in which cone-type coil springs are used as the upper spring157 and the lower spring 158, it is advantageous to improving a ridecomfort and securing an additional free length.

A mount portion may be formed on the top surface of the free piston 120such that the lower end of the upper spring 157 is mounted thereon. Amount portion may be formed on the bottom surface of the free piston 120such that the upper end of the lower spring 158 is mounted thereon. Thelower end of the lower spring 158 is mounted on the fixing member 144 ofthe auxiliary valve assembly 140. As in the case of the main pistonvalve assembly, a Teflon band 129 may be attached to the outercircumferential surface of the free piston 120.

According to the present invention, an inner tube 130, in which a convexportion, a concave portion, a hole, or a cut-out portion is formed, maybe inserted into the housing 110 such that the passage communicating theupper chamber 11 with the lower chamber 12 within the cylinder 10 isopened or closed according to the vertical movement of the free piston120 within the housing 110.

According to the first embodiment of the present invention, the innertube 130 inserted into the housing 110 includes at least one upperconcave portion 131, which is formed concavely on the inner surface ofthe inner tube 130, and at least one lower concave portion 132, which isnot connected to the upper concave portion 131 but is formed in astraight line with the upper concave portion 131. When no external forceis applied, the free piston 120 is disposed between the upper concaveportion 131 and the lower concave portion 132. That is, when no externalforce is applied, the free piston 120 is maintained at a height wherethe concave portion is not formed, and does not allow the flow of theworking fluid between the upper chamber 11 and the lower chamber 12. Tothis end, an internal diameter of the inner tube 130 in a region wherethe concave portion is not formed is substantially equal to an externaldiameter of the free piston 120.

According to the first embodiment of the present invention, when thepassage between the upper space 111 and the lower space 112 is opened,the working fluid pressurizing the free piston 120 flows through thispassage. In other words, according to the first embodiment of thepresent invention, since the working fluid pressurizing the free piston120 flows through the passage to an opposite side of the free piston120, the flow of the working fluid pressurizing the free piston 120 andthe flow of the working fluid passing through the free piston andflowing to the opposite side are formed as a single flow, not separateflows.

Hereinafter, the operation of the valve structure according to the firstembodiment of the present invention will be described with reference toFIGS. 2 and 3.

FIG. 2 shows a position of the free piston 120 at a high frequency (thatis, a small amplitude), and FIG. 3 shows a position of the free piston120 at a low frequency (that is, a large amplitude). When the externalforce, such as the inertia and the pressure of the working fluid, isapplied, the free piston 120 may move while compressing the upper spring157 or the lower spring 158. That is, when the external force applied tothe free piston 120 is strong enough to compress the upper spring 157 orthe lower spring 158, the free piston 120 moves upward or downward.

FIG. 2 shows a state in which the external force applied to the freepiston 120 is not strong enough to compress the upper spring 157 or thelower spring 158 because the movement amplitude of the piston rod of theshock absorber is small and the frequency thereof is high. In a statethat the free piston 120 does not move, the outer surface of the freepiston 120 is in contact with the inner surface of the inner tube 130all over the entire periphery. Therefore, the flow of the working fluidis impossible. In this case, the working fluid of the upper chamber 11may flow to the connection passage 21 formed inside the piston rod 20and the upper space 11, that is, the space above the free piston 120among the inner spaces of the housing 110, but a more flow is impossibleby the free piston 120.

As such, at the high frequency and the small amplitude, the workingfluid can mainly flow through the main piston valve assembly 30.Therefore, the damping force is mainly obtained by the main piston valveassembly 30.

FIG. 3 shows a state in which the external force applied to the freepiston 120 is strong enough to compress the upper spring 157 or thelower spring 158 because the movement amplitude of the piston rod of theshock absorber is large and the frequency thereof is low. In this case,the working fluid of the upper chamber 11 may flow to the lower chamber12 through the connection passage 21 formed inside the piston rod 20,the lower concave portion 132 formed on the inner surface of the innertube 130, and the auxiliary valve assembly 140. The working fluid mayalso flow from the lower chamber 12 to the upper chamber 11. That is,the working fluid of the lower chamber 12 may flow to the upper chamber11 through the auxiliary valve assembly 140, the lower concave portion132 formed on the inner surface of the inner tube 130, and theconnection passage 21 formed inside the piston rod 20.

Although only the state of the rebound stroke is shown in FIG. 3, thefree piston 120 moves upward and the working fluid can flow through theupper concave portion 131, even when the external force applied to thefree piston 120 is strong enough to compress the upper spring 157because the movement amplitude of the piston rod of the shock absorberis large and the frequency thereof is low during the compression stroke.

As such, at the low frequency and the large amplitude, the damping forcecan be obtained by the main piston valve assembly 30 and the auxiliaryvalve assembly 140.

Hereinafter, a valve structure according to a second embodiment of thepresent invention will be described with reference to FIGS. 4 and 5.Since the valve structure according to the second embodiment isdifferent in the frequency unit from the valve structure according tothe first embodiment, a description will focus on the differencetherebetween.

The frequency unit 200 according to the second embodiment includes ahollow housing 210, a free piston 220, and an auxiliary valve assembly240. The inside of the housing 210 is empty, and the housing 210 ismounted at a lower end of the piston rod 20 such that it is disposedunder the main piston valve assembly 30. The free piston 220 opens orcloses a flow passage while moving within the housing 210. The auxiliaryvalve assembly 240 is mounted at a lower end of the housing 210.

The auxiliary valve assembly 240 includes an auxiliary valve body 241,an auxiliary compression valve unit 245, and an auxiliary rebound valveunit 247. The auxiliary valve body 241 has at least one auxiliarycompression passage 242, through which a working fluid passes duringcompression of the shock absorber, and at least one auxiliary reboundpassage 243, through which a working fluid passes during rebound of theshock absorber. The auxiliary compression valve unit 245 is disposedabove the auxiliary valve body 241 to generate a damping force against apressure of the working fluid passing through the auxiliary compressionpassage 242. The auxiliary rebound valve unit 247 is disposed under theauxiliary valve body 241 to generate a damping force against a pressureof the working fluid passing through the auxiliary rebound passage 243.A fixing member 244, including a rivet, a bolt, and a nut, is installedin the middle of the auxiliary valve body 241, such that the auxiliarycompression valve unit 245 and the auxiliary rebound valve unit 27147are disposed above and under the auxiliary valve body 241.

The auxiliary valve body 241 of the auxiliary valve assembly 240 isfixed under the main piston valve assembly 30 by the housing 210. Theinner space of the housing 210, in particular, an upper space 211 abovethe free piston 220, may communicate with the upper chamber 11 through aconnection passage 21 formed inside the piston rod 20. The inner spaceof the housing 210 may be partitioned into the upper space 211 and thelower space 212 by the free piston 220.

The free piston 220 is installed to move vertically within the innerspace of the housing 210 according to a frequency (amplitude). The freepiston 220 is supported within the inner space of the housing 210 by anupper spring 257 as an upper elastic member and a lower spring 258 as alower elastic member. The upper elastic member and the lower elasticmember may be any one selected from a spring, a disk, and a clip. Theupper elastic member and the lower elastic member may be any member thatcan support the free piston 220 by elasticity. The upper spring 257 andthe lower spring 258 as the elastic members may be different in shape ormodulus of elasticity, and various modifications may be made in design.In the case in which cone-type coil springs are used as the upper spring257 and the lower spring 258, it is advantageous to improving a ridecomfort and securing an additional free length.

A mount portion may be formed on the top surface of the free piston 220such that the lower end of the upper spring 257 is mounted thereon. Amount portion may be formed on the bottom surface of the free piston 220such that the upper end of the lower spring 258 is mounted thereon. Thelower end of the lower spring 258 is mounted on the fixing member 244 ofthe auxiliary valve assembly 240. As in the case of the main pistonvalve assembly, a Teflon band 229 may be attached to the outercircumferential surface of the free piston 220.

According to the present invention, an inner tube 230, in which a convexportion, a concave portion, a hole, or a cut-out portion is formed, maybe inserted into the housing 210 such that the passage communicating theupper chamber 11 with the lower chamber 12 within the cylinder 10 isopened or closed according to the vertical movement of the free piston220 within the housing 210.

According to the second embodiment, the inner tube 230 inserted into thehousing 210 has a ring-shaped concave portion 231 that is concavelyformed in a ring shape on the inner surface thereof When no externalforce is applied, the free piston 220 is disposed at a position wherethe ring-shaped concave portion 231 is formed. That is, when no externalforce is applied, the free piston 220 is maintained at a height wherethe concave portion is formed, and allows the flow of the working fluidbetween the upper chamber 11 and the lower chamber 12. On the otherhand, when the external force is applied to move the free piston 220vertically by more than a predetermined distance and thus the freepiston 220 gets out of the region where the ring-shaped concave portion231 is formed, the flow passage of the working fluid between the upperchamber 11 and the lower chamber 12 is closed by the free piston 220. Tothis end, an internal diameter of the inner tube 230 in a region wherethe concave portion is not formed is substantially equal to an externaldiameter of the free piston 220.

Hereinafter, the operation of the valve structure according to thesecond embodiment of the present invention will be described withreference to FIGS. 4 and 5.

FIG. 4 shows a position of the free piston 220 at a low frequency (thatis, a large amplitude), and FIG. 5 shows a position of the free piston220 at a high frequency (that is, a small amplitude). When the externalforce, such as the inertia and the pressure of the working fluid, isapplied, the free piston 220 may move while compressing the upper spring257 or the lower spring 258. That is, when the external force applied tothe free piston 220 is strong enough to compress the upper spring 257 orthe lower spring 258, the free piston 220 moves upward or downward.

FIG. 4 shows a state in which the external force applied to the freepiston 220 is strong enough to compress the upper spring 257 or thelower spring 258 because the movement amplitude of the piston rod of theshock absorber is large and the frequency thereof is low. In a statethat the free piston 220 moves, the outer surface of the free piston 220is in contact with the inner surface of the inner tube 230 all over theentire periphery. Therefore, the flow of the working fluid isimpossible. In this case, the working fluid of the upper chamber 11 mayflow to the connection passage 21 formed inside the piston rod 20 andthe upper space 211, that is, the space above the free piston 220 amongthe inner spaces of the housing 210, but a more flow is impossible bythe free piston 220.

Although only the state of the rebound stroke is shown in FIG. 4, thefree piston 220 moves upward and the flow of the working fluid isimpossible, even when the external force applied to the free piston 220is strong enough to compress the upper spring 257 because the movementamplitude of the piston rod of the shock absorber is large and thefrequency thereof is low during the compression stroke.

As such, at the low frequency and the large amplitude, the working fluidcan mainly flow through the main piston valve assembly 30. Therefore,the damping force is mainly obtained by the main piston valve assembly40.

FIG. 5 shows a state in which the external force applied to the freepiston 220 is not strong enough to compress the upper spring 257 or thelower spring 258 because the movement amplitude of the piston rod of theshock absorber is small and the frequency thereof is high. In this case,the working fluid of the upper chamber 11 may flow to the lower chamber12 through the connection passage 21 formed inside the piston rod 20,the ring-shaped concave portion 232 formed on the inner surface of theinner tube 230, and the auxiliary valve assembly 240. The working fluidmay also flow from the lower chamber 12 to the upper chamber 11. Thatis, the working fluid of the lower chamber 12 may flow to the upperchamber 11 through the auxiliary valve assembly 240, the ring-shapedconcave portion 232 formed on the inner surface of the inner tube 230,and the connection passage 21 formed inside the piston rod 20. As such,at the high frequency and the small amplitude, the damping force can beobtained by the main piston valve assembly 30 and the auxiliary valveassembly 240.

Inner tubes having various shapes are shown in FIGS. 6A to 6D. FIG. 6Ais a perspective view of the inner tube 130 applied to the firstembodiment of the present invention. In the example of FIG. 6A, upperand lower concave portions are formed by pressurizing a cylindrical tubeby a press or the like. An example in which an inner surface isprocessed in a circumferential direction is shown in FIG. 6B. Ifnecessary, a plurality of holes may be formed in the cylindrical tube asshown in FIG. 6C, or the inner tube may be manufactured by formingcut-out portions in upper and lower sides as shown in FIG. 6D.

Hereinafter, a valve structure according to a third embodiment of thepresent invention will be described with reference to FIGS. 7 and 9.Since the valve structure according to the third embodiment is differentin the frequency unit from the valve structure according to the firstembodiment, a description will focus on the difference therebetween.

The frequency unit 300 according to the third embodiment includes ahollow housing 310, a free piston 320, and an auxiliary valve assembly340. The inside of the housing 310 is empty, and the housing 310 ismounted at a lower end of the piston rod 20 such that it is disposedunder the main piston valve assembly 30 a. The free piston 320 opens orcloses a flow passage while moving within the housing 310. The auxiliaryvalve assembly 340 is mounted at a lower end of the housing 310.

Although the main piston valve assembly 30 a of FIG. 7 is shown ashaving a different configuration from the main piston valve assembly 30of FIG. 1, the configurations of the main piston valve assemblies 30 and30 a are merely exemplary and the present invention is not limited bythe configurations of the main piston valve assemblies.

The auxiliary valve assembly 340 includes an auxiliary valve body 341,an auxiliary compression valve unit 345, and an auxiliary rebound valveunit 347. The auxiliary valve body 341 has at least one auxiliarycompression passage 342, through which a working fluid passes duringcompression of the shock absorber, and at least one auxiliary reboundpassage 343, through which a working fluid passes during rebound of theshock absorber. The auxiliary compression valve unit 345 is disposedabove the auxiliary valve body 341 to generate a damping force against apressure of the working fluid passing through the auxiliary compressionpassage 342. The auxiliary rebound valve unit 347 is disposed under theauxiliary valve body 341 to generate a damping force against a pressureof the working fluid passing through the auxiliary rebound passage 343.A fixing member 344, including a rivet, a bolt, and a nut, is installedin the middle of the auxiliary valve body 341, such that the auxiliarycompression valve unit 345 and the auxiliary rebound valve unit 347 aredisposed above and under the auxiliary valve body 341.

Although the auxiliary valve assembly 340 of FIG. 7 is shown as having adifferent configuration from the auxiliary valve assembly 140 of FIG. 1,the configurations of the auxiliary valve assemblies 140 and 340 aremerely exemplary.

The auxiliary valve body 341 of the auxiliary valve assembly 340 isfixed under the main piston valve assembly 30 a by the housing 310. Theinner space of the housing 310, in particular, an upper space 311 abovethe free piston 320, may communicate with the upper chamber 11 through aconnection passage 21 formed inside the piston rod 20. A lower space 312under the free piston 320 may communicate with the lower chamber 12through the auxiliary valve assembly 340. The inner space of the housing310 may be partitioned into the upper space 311 and the lower space 312by the free piston 320.

The free piston 320 is installed to move vertically within the innerspace of the housing 310 according to a frequency (amplitude). The freepiston 320 is supported within the inner space of the housing 310 by anupper spring 357 as an upper elastic member and a lower spring 358 as alower elastic member. The upper elastic member and the lower elasticmember may be any one selected from a spring, a disk, and a clip. Theupper elastic member and the lower elastic member may be any member thatcan support the free piston 320 by elasticity. The upper spring 357 andthe lower spring 358 as the elastic members may be different in shape ormodulus of elasticity, and various modifications may be made in design.In the case in which cone-type coil springs are used as the upper spring357 and the lower spring 358, it is advantageous to improving a ridecomfort and securing an additional free length.

The free piston 320 has a through-hole 325 that is opened during alow-frequency compression to allow the working fluid to flow from thelower space 312 to the upper space 311. If no external force is applied,the through-hole 325 maintains a state closed by a valve body 326. Thevalve body 326 is stacked on the upper surface of the free piston 320.The lower end of the upper spring 357 is mounted on the valve body 326.Accordingly, the valve body 326 is pressurized toward the free piston320. A mount portion may be formed on the bottom surface of the freepiston 320 such that the upper end of the lower spring 358 is mountedthereon. The lower end of the lower spring 358 is mounted on the fixingmember 344 of the auxiliary valve assembly 340.

As in the case of the first and second embodiments, a Teflon band may beattached to the outer circumferential surface of the free piston 320. Onthe other hand, in the third embodiment, a lip portion 329 made of arubber may be integrally formed. The lip portion 329 may closely contactthe inner surface of the housing 310 and perform a sealing function.

According to the third embodiment, instead of inserting the separateinner tube into the housing 310, a stepped portion 313 and a pluralityof groove portions 314 may be directly formed on the inner surface ofthe housing 310 when needed. Accordingly, as the free piston 320 movesvertically within the housing 310, the passage communicating the upperchamber 11 with the lower chamber 12 within the cylinder 10 may beopened or closed.

According to the third embodiment, the stepped portion 313 limiting themovement of the free piston 320 is formed on the inner surface of theupper space 311 of the housing 310. The plurality of groove portions 314are formed on the inner surface of the lower space 312 of the housing310. An intermediate portion 315 is formed between the stepped portion313 and the groove portion 314 on the inner surface of the housing 310.The intermediate portion 315 has an internal diameter substantiallyequal to an external diameter of the free piston 320, more specifically,an external diameter of the lip portion 329 integrally formed at acircumferential edge of the free piston 320. When no external force isapplied, the free piston 320 is disposed at the intermediate portion 315of the housing 310.

When no external force is applied, the free piston 320 is disposed atthe intermediate portion 315. Accordingly, the free piston 320 does notallow the flow of the working fluid between the upper chamber 11 and thelower chamber 12. On the other hand, when the external force is appliedto move the free piston 320 downward by more than a predetermineddistance and thus the free piston 315 gets out of the intermediateportion 315, the working fluid may flow through the groove portions 314.In addition, when the external force is applied to move upward the valvebody 326 stacked on the upper surface of the free piston 320 whilecompressing the upper spring 357, the through-hole 325 is opened toallow the flow of the working fluid.

According to the third embodiment of the present invention, when thepassage between the upper space 311 and the lower space 312 is opened,the working fluid pressurizing the free piston 320 flows through thispassage.

In other words, according to the third embodiment of the presentinvention, since the working fluid pressurizing the free piston 320flows through the passage to an opposite side of the free piston 320,the flow of the working fluid pressurizing the free piston 320 and theflow of the working fluid passing through the free piston 320 andflowing to the opposite side of the free piston 320 are formed as asingle flow, not separate flows.

Hereinafter, the operation of the valve structure according to the thirdembodiment of the present invention will be described with reference toFIGS. 7 and 9.

FIG. 7 shows a position of the free piston 320 in an initial state inwhich no external force is applied. FIG. 8 shows a position of the freepiston 320 during a low-frequency (that is, large-amplitude)compression, and FIG. 9 shows a position of the free piston 320 during alow-frequency (that is, large-amplitude) rebound. When the externalforce, such as the inertia and the pressure of the working fluid, isapplied, the free piston 320 may move while compressing the upper spring357 or the lower spring 358. That is, when the external force applied tothe free piston 320 is strong enough to compress the upper spring 357 orthe lower spring 358, the free piston 320 moves upward or downward.

FIG. 7 shows a state in which the external force applied to the freepiston 320 is not strong enough to compress the upper spring 357 or thelower spring 358 because the movement amplitude of the piston rod of theshock absorber is small and the frequency thereof is high. In a statethat the free piston 320 is located at the intermediate portion 315, theouter surface of the free piston 320 is in contact with the intermediateportion 315 of the inner surface of the housing. Therefore, the flow ofthe working fluid between the upper space 311 and the lower space 312 isimpossible.

FIG. 8 shows a state in which the external force applied to the freepiston 320 is strong enough to compress the upper spring 357 because thedownward-movement amplitude of the piston rod of the shock absorber islarge and the frequency thereof is low. When the free piston 320 movingwhile compressing the upper spring 257 comes into contact with thestepped portion 313, further movement of the free piston 320 is limited.In this case, when the external force is continuously applied, the valvebody 326 closing the through-hole 325 moves while further compressingthe upper spring 357. Accordingly, the through-hole 325 is opened, andthe working fluid may flow from the lower space 312 to the upper space311.

FIG. 9 shows a state in which the external force applied to the freepiston 320 is strong enough to compress the upper spring 358 because theupward-movement amplitude of the piston rod of the shock absorber islarge and the frequency thereof is low. When the free piston 320 movingwhile compressing the lower spring 358 moves down to a region where thegroove portion 314 is formed, the passage allowing the flow of theworking fluid is opened and thus the working fluid can flow to the lowerspace 312.As described above, the present invention can provide a valvestructure of a shock absorber, which includes a main piston valveconfigured to generate a damping force varying according to a movingspeed of a piston, and a frequency unit configured to generate a dampingforce varying according to a frequency.

Therefore, the valve structure of the shock absorber according to thepresent invention can satisfy both the vehicle ride comfort and thesteering stability.

While the valve structure of the shock absorber according to the presentinvention has been described with reference to the specific embodiments,it will be apparent to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the following claims.

1. A valve structure of a shock absorber including a cylinder filledwith a working fluid and a piston rod having one end located inside thecylinder and the other end extending outward from the cylinder, thevalve structure comprising: a main piston valve assembly installed atone end of the piston rod and configured to operate in a state that theinside of the cylinder is divided into an upper chamber and a lowerchamber, and generate a damping force varying according to a movingspeed; and a frequency unit configured to move together with the mainpiston valve assembly and generate a damping force varying according toa frequency, wherein the frequency unit comprises: a hollow housingmounted at a lower end of the piston rod such that the housing isdisposed under the main piston valve assembly; a free piston disposed tobe vertically movable within the housing; and an auxiliary valveassembly mounted at a lower end of the housing, and an inner space ofthe housing is partitioned into an upper space and a lower space by thefree piston.
 2. The valve structure according to claim 1, wherein a flowof a working fluid pressurizing the free piston and a flow of a workingfluid passing through the free piston and flowing to an opposite side ofthe free piston are formed as a single flow.
 3. The valve structureaccording to claim 1, wherein the upper space communicates with theupper chamber through a connection passage formed inside the piston rod,and the lower space communicates with the lower chamber through theauxiliary valve assembly amounted at the lower end of the housing. 4.The valve structure according to claim 1, wherein the free piston has athrough-hole that is opened during a low-frequency compression to allowthe working fluid to flow from the lower space to the upper space, andwhen no external force is applied, the through-hole maintains a stateclosed by a valve body.
 5. The valve structure according to claim 1,wherein a lip portion made of a rubber is integrally formed on an outercircumferential surface of the free piston, and the lip portion closelycontacts an inner surface of the housing.
 6. The valve structureaccording to claim 1, wherein a stepped portion limiting the movement ofthe free piston is formed on an inner surface of the upper space of thehousing, a plurality of groove portions are formed on an inner surfaceof the lower space of the housing, and an intermediate portion having aninternal diameter substantially equal to an external diameter of thefree piston is formed between the stepped portion and the grooveportion.
 7. The valve structure according to claim 1, wherein thefrequency unit comprises an inner tube installed inside the housing toopen or close a flow passage in cooperation with the free piston.
 8. Thevalve structure according to claim 7, wherein the inner tube comprisesat least one of a convex portion, a concave portion, a hole, or acut-out portion, such that a passage communicating the upper chamberwith the lower chamber within the cylinder is opened or closed accordingto a vertical movement of the free piston within the housing.
 9. Thevalve structure of claim 7, wherein the inner tube comprises at leastone upper concave portion, which is concavely formed on an inner surfaceof the inner tube, and at least one lower concave portion, which is notconnected to the upper concave portion and is formed in a straight linewith the upper concave portion, and when no external force is applied,the free piston is located between the upper concave portion and thelower concave portion.
 10. The valve structure of claim 8, wherein theinner tube comprises a ring-shaped concave portion that is concavelyformed on the inner surface in a ring shape, and when no external forceis applied, the free piston is located at a position where thering-shaped concave portion is formed.
 11. The valve structure accordingto claim 1, wherein the free piston is supported by an upper elasticmember and a lower elastic member, such that the free piston movesvertically within the inner space of the housing according to afrequency.